[paulojreis]

I haven't read everything in detail, but this reminded me of the API developed for modal dialogs. It ended like this:

https://dev.opera.com/blog/showmodaldialog/

Both the ideas seem good, but it's hard to not think about "Embrace, extend and extinguish".

[pvg]

The sidebar API is for chrome extensions, not web pages. They're probably not extending their own API in order to extinguish it.

[paulojreis]

You're right. I haven't noticed that the API was "chrome.sidebar".